The lady suddenly collapsed and started fitting just after midday in the biscuit aisle of Waitrose in Marmion Road, Southsea.
An ambulance was called at 12.20pm as staff closed off the aisle and tended to her until ambulance arrived.
She was then rushed to Queen Alexandra Hospital where she is currently undergoing further assessment and treatment.
The woman's husband arrived at the store and found out Waitrose had paid for their shopping.
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A spokesman for South Central Ambulance Service said: ‘We were called to a medical emergency at the store around 12.20pm today and took one patient to the hospital for further assessment and treatment.’
